Everyone is very different with what levels are acceptable and/or achievable. Just remember Metformin is by no means a solution on it’s own, you still need to watch what you eat, especially carbs and of course sugar.
I take Metformin and restrict my carbs to under 45g/day and have achieved HbA1cs in the 30s since a few months after diagnosis. However as I said we can’t suggest levels you should achieve on your dose of Metformin as we are all different.